Ensure widgets bindings are initialized

[algodave]

On Flutter 1.9.5 I was getting the following error on await DotEnv().load('.env'):

ServicesBinding.defaultBinaryMessenger was accessed before the binding was initialized.

After reproducing the error in a sample app Flutter gave me an explanatory error message with the solution:

E/flutter (19823): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: ServicesBinding.defaultBinaryMessenger was accessed before the binding was initialized.
E/flutter (19823): If you're running an application and need to access the binary messenger before `runApp()` has been called (for example, during plugin initialization), then you need to explicitly call the `WidgetsFlutterBinding.ensureInitialized()` first.
E/flutter (19823): If you're running a test, you can call the `TestWidgetsFlutterBinding.ensureInitialized()` as the first line in your test's `main()` method to initialize the binding.

So I added WidgetsFlutterBinding.ensureInitialized() before calling rootBundle.loadString()

[java-james]

Thanks for the PR. Letting you know I've seen it and will review it with you before the end of the week.

[java-james]

Merged, released, tagged & published to pub. Thanks for the contribution @algodave